More N3077 raw string changes
	* charset.c (cpp_interpret_string): Don't transform UCNs in raw
	strings.
	* lex.c (bufring_append): Split out from...
	(lex_raw_string): ...here.  Undo trigraph and line splicing
	transformations.  Do process line notes in multi-line literals.
	(_cpp_process_line_notes): Ignore notes that were already handled.

From-SVN: r157804